From my understanding the threshold between recreational diving and intermediate technical diving starts with taking the courses in Advanced Nitrox and Decompression Procedures, resetting your dive computer to have two forms of gas, a stage bottle or deco bottle, and a regulator that can breath 80% nitrox.

Hence, you need to throw away your basic dive computer which no longer can be used for dual gas situations. Yes, there are many readers out there that want to simplify or complicate the above statements, but this appears the threshold.